1. Field of the Invention
The present invention relates to an antenna system.
2. Description of Related Art
Conventionally, if an antenna system is to receive a television broadcasting signal (hereinafter, “TV broadcasting signal”), a user, for example, adjusts a direction and the like of an antenna while referring to an image displayed on a display section so that the antenna is oriented to an optimum receiving direction. This adjustment method, however, is quite cumbersome to a user. To deal with the problem, the following antenna systems are proposed. For example, Japanese Patent Application Laid-Open No. 2001-94899 discloses an antenna system that includes an indicator that can display a reception status of a TV broadcasting signal. A user can manually adjust a direction and the like of an antenna while referring to the reception status displayed by the indicator. Further, Japanese Patent Application Laid-Open No. 2001-86019 discloses an antenna system that can automatically adjust a direction and the like of an antenna in response to a request from a user.
There is also proposed an antenna system that includes an antenna apparatus having an antenna (commonly known “smart antenna”) capable of automatically switching directivity of the antenna whenever a user designates a desired channel, and a television receiver. Specifically, the antenna apparatus is controlled by the television receiver based on a predetermined specification according to EIA/CEA-909 or the like to switch the directivity or the like of the smart antenna.
There has been established a method of deciding an optimum receiving direction of the smart antenna for a digital TV broadcasting signal using an intensity of the signal and an error rate. However, a method of deciding an optimum receiving direction of the smart antenna for an analog TV broadcasting signal is not established yet.
To deal with the problem, therefore, the following antenna systems are proposed. For example, Japanese Patent Application Laid-Open No. 2005-354435 discloses an antenna system that obtains horizontal synchronizing signals while sequentially switching the directivity of a smart antenna and determines one direction in which a center angle of a region in which the horizontal synchronizing signals can be continuously obtained is bisected as an optimum receiving direction of the smart antenna. If there are two or more regions in which the horizontal synchronizing signals can be continuously obtained, the antenna system determines one direction in which a greatest center angle is bisected as the optimum receiving direction of the smart antenna. Further, Japanese Patent Application Laid-Open No. 2005-318140 discloses an antenna system that determines one direction in which complexity of an image based on image data obtained from a received analog TV broadcasting signal is lowest as an optimum receiving direction of a smart antenna.
Although the proposed method disclosed in the Japanese Patent Application Laid-Open No. 2005-354435 is simple, the determined direction, in which a center angle of a region in which the horizontal synchronizing signals can be continuously obtained is bisected, is not always an optimum receiving direction. Therefore, it is difficult to accurately determine an optimum receiving direction.
The technique disclosed in the Japanese Patent Application Laid-Open No. 2005-318140 has the following problems. The optimum receiving direction determined when, for example, an image is greatly changed is not always an actual optimum receiving direction. Therefore, it is difficult to accurately determine an optimum receiving direction. Furthermore, with this method, it takes long operation time because it is necessary to carry out an image processing to determine the optimum receiving direction.